The present invention relates to a method for preparing phthalimides. In particular, this invention relates to an environmentally friendly, solventless method for the preparation of tris(phthalimide)s, bis(phthalimide)s, mono(phthalimide)s, and mixtures thereof.
Tris(phthalimide)s, bis(phthalimide)s and mono(phthalimide)s are useful branching monomers, polymerizable monomers and end-capping monomers, respectively, for polymer synthesis. For example, chlorophthalimides are useful as intermediates in the synthesis of condensation polymers. The bis(chlorophthalimide) having the formula (I) is a polymerizable monomer useful in the synthesis of polyetherimides: ##STR1## The phthalimide of formula (I) is typically prepared by catalysis under conditions of total reflux in glacial acetic acid or in other organic solvents from which the water of reaction is removed by azeotropic distillation. Typically, the solid monomer is only soluble up to about 2% by weight, and thus cannot be readily used in situ, but must be isolated by filtration, washing and drying.
Many different phthalimides are typically made using solvent-based processes. The use of solvents presents environmental and cost concerns. One commonly used organic solvent in such processes is o-dichlorobenzene, which is not environmentally benign. Other, more environmentally benign solvents have been examined, but have been found to provide in general slower reaction, less conversion to product, and more impurities than are desirable in a manufacturing situation.
Accordingly, there remains a need for improved, environmentally sound, economical methods for producing phthalimides such as mono-, bis-, and tris(chlorophthalimide)s. Such methods must also have good reaction rates and high percent conversion to a product isolable in a convenient, usable physical form.